Loyal to His Mate by Haley Weir

When Peyton finds out that she is a wolf shifter, the surprises don’t stop there.

Unfortunately, most of the surprising events that follow aren’t good ones. Not only have all eighteen years of her life been a lie, but the people she knows aren’t exactly what they seem to be—especially not the gorgeous looking man that has been following her.
The last thing that Jasper had planned on, was running across Peyton and having his entire life turned upside-down.
But after he claims her as his mate, his allegiance shifts from serving his alpha, to protecting the woman he loves from the shadow world that threatens to exert dominion over them all.
Fortunately, Jasper is strong enough to take on any threat that comes for them, even if that threat is his own alpha.
At least until his one weakness is discovered and used against him, the one thing that can bring him to his knees—Peyton.